1. Field of the Invention
The invention relates generally to the field of photography, and in particular to a film cassette containing a film spool about which a filmstrip is coiled. More specifically, the invention relates to a film cassette having a spool lock for preventing unintended rotation of the film spool.
2. Description of the Prior Art
Film cassettes provided with a spool lock for preventing unintended rotation of a film spool inside the cassette are generally known.
For example, U.S. Pat. No. 4,221,479 issued Sep. 9, 1980 discloses a film cassette adapted to be opened and closed comprising a film spool supported for rotation, and movable locking means for inhibiting rotation of the film spool when the cassette is closed and allowing the film spool to rotate when the cassette is opened. The film cassette has a pair of collar halves at each end of the cassette with respective polygon-shaped bearing halves for receiving polygon-shaped journals at opposite ends of the film spool. When the film cassette is closed, rotation of film spool is inhibited because of the contact between the bearing halves and the journals. Conversely, when the film cassette is opened, the film spool is free to rotate because bearing halves have been moved away from the journals.
According to another example, U.S. Pat. No. 5,115,268 issued May 19, 1992 discloses a film cassette comprising a light-trapping plush for preventing ambient light from entering the cassette interior through a film egress/ingress passageway, a film spool supported for rotation in film unwinding and film winding directions, and a locking pawl supported for movement into engagement with the film spool to secure the spool and out of engagement with the spool to release the spool. The film spool has a coaxial ratchet wheel with asymmetrically shaped teeth. The locking pawl appears to be a rigid beam member which is pivotally mounted at one end and has an asymmetrically shaped detent portion at an opposite end. A curved spring arm portion of the locking pawl extends from the end of the rigid beam member that has the detent portion, to bias the detent portion to between any two adjacent ones of the teeth in order to secure the film spool. To remove the detent portion from between two adjacent ones of the teeth, an engagement release portion of the locking pawl is turned to pivot the rigid beam member against the contrary urging of the spring arm portion. The engagement release portion then is held in the turned-to position to maintain the detent portion separated from the ratchet wheel. When the engagement release portion is released, the spring arm portion is free to pivot the rigid beam member to return the detent portion to between any two adjacent ones of the teeth in order to re-secure the spool.